The present invention relates to thermostatically actuated electrical switches and in particular to such switches having a single pole double throw type of switching function. Switches of this type are often employed in the programming control system for household appliances such as washing machines and dishwashers.
In applications for domestic applicances, it is sometimes required to employ an SPDT switch wherein one set of contacts is required to switch a relatively high current load, whereas, the other set of contacts will be required to switch only a very light current load. In such applications, it has been found desirable to limit the contact forces of the two sets of contacts to the absolute minimum in order to reduce the force required to actuate the switch mechanism. This is particularly a problem area in designing switches for applications requiring a high degree of thermal sensitivity where the thermal sensing means is able to provide only a minimum force for actuating the electrical switching mechanism.
Where one set of contacts of the switch is utilized for switching very low current and has a low contact force, it has been found desirable to provide the contacts with a wiping action to remove any accumulation of oxidation deposits on the contact surfaces from lowering the surface conductivity of the contacts.
In applications where one set of contacts is required to switch high current loads, it is desirable to have the switching performed in a snap-action mode to prevent arcing and burning of the contacts.
Thus, it has been desired to provide an SPDT switch having the capability of switching a low current load on one set of contacts and providing a wiping motion thereto; and yet provide the other set of contacts with the snap-action required to switch a high current load.
Heretofore, it has been difficult to provide such an SPDT which is capable of being actuated by a low force output thermally responsive actuator in applications where the switch is employed as a thermostatic switching controller and combine high current switching and low current switching while maintaining a high degree of thermal sensitivity for the control function.